The present invention relates generally to gas turbine engines, and, more specifically, to exhaust nozzles therein.
In a gas turbine engine, air is pressurized in a compressor and mixed with fuel in a combustor for generating hot combustion gases. Energy is extracted from the gases in a high pressure turbine (HPT) which powers the compressor, and, additional energy is extracted from the gases in a low pressure turbine (LPT) which powers an upstream fan in a turbofan aircraft engine application.
In the turbofan engine, a bypass duct surrounds the core engine and bypasses pressurized fan air through a fan nozzle for providing a large portion of propulsion thrust. Some of the fan air enters the core engine wherein it is further pressurized to generate the hot combustion gases which are discharged through the primary or core exhaust nozzle to provide additional propulsion thrust concentrically inside the surrounding fan air stream.
During takeoff operation of the engine in an aircraft, the high velocity core exhaust and fan exhaust generate significant noise as the exhaust flows mix with the ambient airflow. Noise attenuation in commercial aircraft engines is a significant design objective that may adversely impact engine efficiency, which is the paramount design objective in commercial aircraft.
The typical core and fan exhaust nozzles are conical and taper in diameter aft to thin, annular trailing edges. The nozzles may be single-ply sheet metal, or may be two-ply sheet metal with a honeycomb strengthening core laminated therebetween.
The nozzles are also typically formed as full, or substantially complete, annular rings which enhances their structural rigidity and strength for accommodating the large pressure loads developed during operation as the core and fan exhaust streams are discharged from the engine at high velocity.
A significant advancement in noise attenuation while maintaining aerodynamic efficiency is found in the chevron exhaust nozzle disclosed in U.S. Pat. No. 6,360,528, assigned to the present assignee. In this Patent, a row of triangular chevrons form the exhaust nozzle for enhancing mixing between the high velocity exhaust flow and the lower velocity surrounding stream. The individual chevrons are integrally formed at the aft end of a supporting annular exhaust duct and enjoy the combined structural rigidity and strength therewith.
During continuing development of the chevron exhaust nozzle, two-ply construction of the chevrons is desirable for aerodynamic performance, yet presents significant problems in the manufacture thereof. The two skins should be smooth and flush for maximizing aerodynamic efficiency of the internal and external flow streams, while the serpentine trailing edge of the chevrons should minimize aerodynamic losses as the expanding inner stream is discharged through the corresponding diverging slots between adjacent chevrons.
Furthermore, the unitary configuration of the annular chevrons nozzle increases the difficulty of manufacture since accidental damage or out of specification manufacture of the individual ones of the full row of chevrons can adversely affect performance of the entire chevron nozzle.
Accordingly, it is desired to provide an improved chevron exhaust nozzle for addressing these performance and manufacturing problems.